A station manager has described the "horrific" scene he encountered after a Greyhound bus carrying 19 people rolled onto its side on a remote Northern Territory highway.

The Royal Flying Doctor Service flew 10 people, including two children, to Alice Springs hospital for further treatment after the crash, which happened 130 kilometres north of Tennant Creek at 5.30am (ACDT) on Friday.

The office manager at the Helen Springs Station, Garret Goring, was one of the first people on the scene.

He said a "freak storm" had passed through the area shortly before, and the bus had skidded after hitting a patch of water.

"[It] caused the bus to aquaplane across the road and [it] just lost control and ended up on its side," he told 783 ABC Alice Springs.

"Quite [a] horrific sort of scene."

He said a truck driver used his vehicle to block the highway so that rescuers could help the injured.

"Basically a lot of people that just needed support," he said.

"There were some serious injuries, we were doing our best just to keep them calm.

"Because it was still raining people were trying their best to keep out of the weather."

'One of the worst'

He said about 50 millimetres of rain fell during the storm.

"This was a freak storm last night.

"It's probably one of the worst that I've seen go through here, even locals would have had trouble with it."

A crane had to be used to lift the bus off a 37-year-old man who was trapped beneath it for two hours. He underwent surgery in Alice Springs on Friday night.

He and another passenger are in a serious but stable condition in the hospital's intensive care unit.

A further three people were to stay in hospital overnight.

Greyhound chief executive, Robert Thomas, said the bus left Alice Springs at 7.30pm and was on its way to Darwin when it rolled.

He said an emergency signal was set off, possibly by someone on the bus or by a passing motorist after the crash.

Greyhound said 23 passengers were booked to travel on the bus, but fewer passengers actually boarded it.

Police say there were 19 people on the bus, including three children and the bus driver.

Mr Thomas said Greyhound was sending two additional buses to the area to pick up passengers capable of continuing their journey.

He said the bus driver had taken a rest stop in Tennant Creek prior to the incident.